This invention relates in general to methods and equipment for testing circuit breaker with electronic trip units. In the past, such testers have been portable units for on-site testing of circuit breakers. The present invention relates to a circuit breaker unit that is integrally provided with a tester circuit to eliminate the need for the portable unit.
The present invention provides an improved system and method for testing the operation a circuit breaker (10), particularly an industrial-type circuit breaker. FIG. 1 illustrates a conventional circuit breaker. As shown in FIG. 1, the exterior of the circuit breaker (10) may be a housing made up of two connected pieces, a case (11) and a cover (12). A switch (15) extends through an opening (14) in the cover (12). The switch (15) can be used to manually operate the circuit breaker (10) to interrupt or re-establish the flow of electricity passed the breaker (10).
A raised portion (13) of the cover (12) includes the opening (14) through which the switch (15) extends. The raised portion (13) may also include an accessory access door (16) for field-installation of a selected accessory to the circuit breaker (10). Accessories can enhance the functionality and operations of the circuit breaker (10).
A rating plug (17) may also be provided in the cover (12) of the housing. These circuit breakers (10) have a removable rating plug (17) that is interconnected with the circuit breaker trip unit by means of a 20-pin connector. The current rating of the breaker (10) may be readily changed by using a different rating plug, which consists of a plurality of resistive elements that are connected by connector terminals to the various sensing circuits in the trip unit of the breaker (10).
In order to allow testing of the circuit breaker (10), the rating plug (17) preferably includes a test jack receptacle (19) and a light-emitting diode (LED) (18). Conventionally, equipment for testing the circuit breaker (10) is connected to the breaker (10) through the test jack receptacle (19). The diode (18) can be lit to indicate that testing equipment is operatively connected to the circuit breaker (10) through the test jack receptacle (19).
In addition to being factory tested, power circuit breakers (10) are operationally tested in the field, typically under low voltage conditions, to verify their proper operation and capability for tripping rated fault currents in a prescribed time. Such testing may occur when the circuit breaker (10) is first installed and then periodically throughout the life of the circuit breaker (10) to ensure continued successful operation.
Three general types of testing are performed: (1) the complete circuit breaker (10) can be tested with a high current (normally at low voltage) designed to cause a trip, (2) the trip circuitry can be tested by injection testing in which test signals, simulating signals from the breaker""s sensors, are input to the circuit breaker (10) which the trip circuitry should detect and respond to accordingly; and, finally, (3) the internal digital circuits of the breaker (10) can be tested with various digital tests.
Circuit breakers have for sometime incorporated internal digital test circuitry for performing the third type of testing. However, the first two types of testing, particularly the injection testing, typically require technicians to bring expensive and cumbersome test equipment to the location of the circuit breaker (10) for connection to the breaker (10) through the test jack receptacle (19).
FIG. 2 illustrates a piece of test equipment (20) that is brought to the location of the circuit breaker (10) and connected to the breaker (10) by a cable (27). The test unit (20) includes a housing (21) with a test jack receptacle (25) therein. The cable (27) connects to the test jack receptacle (19) of the breaker (10) and, with a jack (26), to a second test jack receptacle (25) in the test unit (20). Conventionally, the cable (27) has a non-standard connector for mating with the test jack receptacle (19). A secondary receptacle (134) may also be provided for connecting additional equipment to the test unit (20).
The status and operational data of the test unit (20) can be displayed on a display (22), e.g., a liquid crystal display (LCD). Various buttons (23A, 23B) and LEDs (24) allow the user to operate the test unit (20), controlling the injection of test signals to the breaker (10) and monitoring the result.
Such portable test units as described above are well known in the art. For example, conventional test units for circuit breakers are described in U.S. Pat. No. 4,814,712 for xe2x80x9cTest Kit for a Circuit Breaker Containing an Electronic Trip Unitxe2x80x9d to Burton et al.; U.S. Pat. No. 5,272,438 for xe2x80x9cField Test Unit for Circuit Breakerxe2x80x9d to Stumme; U.S. Pat. No. 5,825,643 for xe2x80x9cProgramming Device for a Circuit Breakerxe2x80x9d to Dvorak et al.; and U.S. Pat. No. 5,872,722 for xe2x80x9cApparatus and Method for Adjustment and Coordination of Circuit Breaker Trip Curves Through Graphical Manipulationxe2x80x9d to Oravetz et al. Each of these documents is incorporated herein by reference in its entirety.
Despite the advantages of being able to field test circuit breakers, the above-described portable test units have a number of disadvantages. First, the portable test units must be purchased, maintained and stored when not in use. Second, the portable test units must be carried with a technician to the site of the circuit breaker to be tested. Third, the portable units must be hardwired through a non-standard connection cable to the circuit breaker.
Consequently, there is a need in the art for an improved method and system for performing on-site, in-the-field injection testing of a circuit breaker.
The present invention meets the above-described needs and others. Specifically, the present invention provides an improved method and system for performing on-site, in-the-field injection testing of a circuit breaker without requiring a dedicated, portable test unit.
Additional advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The advantages of the invention may be achieved through the means recited in the attached claims.
The present invention may be embodied and described as a circuit breaker including trip circuitry; a microprocessor; and an analog test signal generator incorporated in the circuit breaker for providing test signals to the trip circuitry under control of the microprocessor. Preferably, the test signal generator includes both a current source and a voltage source for generating the test signals.
A standard interface on the circuit breaker is connected to the microprocessor and allows the breaker to be connected to a corresponding standard interface on a general purpose computing device. The general purpose computing device can then be used to initiate and regulate testing of the circuit breaker. Alternatively, the interface with the general purpose computing device may be a wireless interface.
The circuit breaker may also have a network interface connected to the microprocessor for connecting the microprocessor to a data network for receipt of commands and transmission of test result data.
A switch may be placed in the connection between the trip circuitry and the test signal generator. The switch is preferably controlled by the microprocessor and is kept open when the trip circuitry is not being tested so as to prevent erroneous test signals from causing a response by the trip circuitry.
Alternatively, a receptacle may form a gap in the connection between the trip circuitry and the test signal generator. A key is then selectively inserted in the receptacle to bridge the gap allowing communication between the trip circuitry and the test signal generator. The key may be a rating plug.
The present invention also encompasses the methods of making and using the circuit breaker described above. For example, the present invention encompasses a method of testing a circuit breaker by testing trip circuitry of the circuit breaker with test signals generated with an analog test signal generator that is incorporated in the circuit breaker.